Semiconductor electronic circuit with overvoltage protection device

Abstract: A semiconductor electronic circuit with a protection device against supply voltage overloading, being of the type which comprises a first power circuit portion (2) connected to a power supply line (AL) and enabled through at least a first transistor (Q1). This transistor (Q1) has a control terminal driven by a voltage sensor (R1, R2, Z1) connected to the power supply line (AL). The semiconductor electronic circuit (1) is characterized, moreover, in that it comprises a second signal circuit portion (3) connected to the power supply line (AL) in a structurally independent manner of the first power circuit portion (2) and through a controlled switch (M1).

Description: This invention relates to semiconductor electronic circuits installed in motor vehicles, and in particular to a semiconductor electronic circuit provided with a protection device against power supply over voltages. The applicative field of the invention is particularly related to the automotive industry, and this description will cover a semiconductor electronic circuit provided with a protection device against supply voltage overloading for the sole purpose of simplifying its illustration. As is well known, semiconductor electronic circuits installed in motor vehicles are to support pulsive supply voltages much in excess of the supply voltage normally applied to them from the vehicle own battery. These supply voltage pulses can be quite high and are commonly referred to as "dump" voltages. They become manifest especially as the connection between the vehicle battery and the motor is opened while the motor is running. Under such circumstances, the battery-charging alternator can generate voltage pulses. It should be pointed out that during the time period when these voltage pulses are generated, the electronic circuits should be stopped, and thereafter resumed as soon as the pulses are over. The electronic circuits installed in motor vehicles are customarily provided with protection devices to prevent their destruction on the occurrence of such voltage pulses. An electronic circuit equipped with a protection device of this kind which embodies the prior art is shown in Figure 1. With reference to this Figure, generally indicated at 1 is an electronic circuit which comprises a protection device 5 incorporating a voltage sensor (R1, R2, Z1) connected between a power supply line AL and a fixed voltage reference GND. In particular, this voltage sensor (R1, R2, Z1) comprises first R1 and second R2 resistive elements connected in series with each other, respectively between the power supply line AL and a first terminal of a zener diode Z1. The zener diode Z1, in turn, has a second terminal connected to the fixed voltage reference GND. Also with reference to Figure 1, the protection device 5 comprises a transistor Q1 of the PNP type, for example, having a control terminal connected to a first circuit node A interconnecting the first R1 and second R2 resistive elements. The transistor Q1 also has a first terminal connected to the supply line AL and a second terminal for enabling protection means included in a circuit portion 4 connected to the same supply line AL. This circuit portion 4 comprises both power and signal elements incorporated to the electronic circuit 1. The electronic circuit 1 operates as follows. With normal supply voltages Vcc, the transistor Q1 is cut off. Under this condition, if the supply voltage Vcc increases, the voltage across the first resistive element R1 also increases. As the supply voltage Vcc exceeds a given threshold value, the transistor Q1 goes from a cut off state over to a conduction state, thereby enabling the protection means arranged within the circuit portion 4 to prevent destruction of the electronic circuit 1. Specifically, such protection means will be operative within the circuit portion 4: 1) to turn off all the current generators; 2) to connect the base terminals of the bipolar transistors to their emitters, thereby utilizing the fact that the value of the breakdown voltage V cbo of the base-collector junction is greater than the breakdown voltage value V ce0 of the collector-emitter junction in the open base terminal condition; the last-mentioned voltage value should be more than the overvoltage value; and 3) to prevent subjecting the MOS transistors to higher gate-source terminal voltages than the values which may result in rupture of the gate oxide. These values are typically on the order of 20 volts. In addition, said MOS transistors should be able to support dump voltages. The circuit portion 4 should be arranged to have all the components therein which are directly or indirectly connected to the supply voltage Vcc, such as resistors, capacitors, and EPI wells, made with sufficiently large tolerances, i.e. sufficient distances between different diffused regions. Furthermore, these components should be designed with layout rules effective to prevent breakdowns from occurring at the transistor junctions due to Zener effect or current losses from parasitic MOS transistors. All of the above protective measures, while being essential to avoid destruction of the electronic circuit 1, do bring about an increase in the silicon area occupied by the circuit structure. In addition, errors become more likely to be introduced due to the large number of rules that the aforesaid protective measures involve. Document EP-A-0 019 864 discloses a power generation control system for regulating the voltage generated at the output by a vehicle alternator and fed to a battery and having the features of the preamble of claim 1. The power generation control system comprises a power circuit having the aim of regulating the operation of the generator. In case of an interruption on the supply line connecting the alternator to the battery, the voltage on the supply line increases and the voltage on the battery drops. In this situation, to avoid damages to users connected to the alternator output, a voltage detector is connected to the supply line and switches off a power circuit and thus the generator. Document DE-A-41 10 495 discloses a circuit for protecting a user from load-dump voltages generated by a generator-battery set. A transistor switch connects a user to the generator-battery set in normal operating conditions. A detector connected to the generator-battery set comprises a voltage sensor and controls a disabling transistor for turning off the transistor switch when the output voltage of the generator-battery set exceeds a preset value. The underlying technical problem of this invention is to provide a semiconductor electronic circuit equipped with a protection device against power supply over voltages, which can remedy the problems connected with the practical circuit implementation of the basic protective measures, in order to prevent the circuit from being destroyed. Furthermore the protective device should not draw any additional quiescent current. The solution according to the invention is defined in claim 1. The features and advantages of the electronic circuit of this invention will be apparent from the following description of an embodiment thereof, given by way of example and not of limitation with reference to the accompanying drawings. In the drawings: Figure 1 shows a diagram for a semiconductor electronic circuit provided with a protection device against supply voltage overloading, according to the prior art; Figure 2 shows a diagram for a semiconductor electronic circuit with a protection device against supply voltage overloading, according to this invention. With reference to the drawing figures, generally and schematically indicated at 1 is a semiconductor electronic circuit with a protection device against power supply over voltages. With reference in particular to Figure 2, the electronic circuit 1 includes a protection device 6 which incorporates a voltage sensor (R1, R2, Z1) connected between a power supply line AL and a fixed voltage reference GND. More particularly, this sensor comprises first R1 and second R2 resistive elements connected in series with each other, between the power supply line AL and a first terminal of a zener diode Z1. The zener diode Z1 is, in turn, provided with a second terminal connected to the fixed voltage reference GND. Also with reference to Figure 2, the protection device 6 further comprises a first transistor Q1 of the PNP type, for example, which has a control terminal connected to a first circuit node A interconnecting the first R1 and second R2 resistive elements. This first transistor Q1 is further provided with a first terminal connected to the power supply line AL and a second terminal for enabling protection means incorporated to a first power circuit portion 2 of the electronic circuit 1 connected to the same power supply line AL. It can be seen in Figure 2 that the protection device 6 also comprises a second transistor Q2 of the PNP type, for example, having first and second terminals respectively connected to the power supply line AL and a second circuit node B, and a control terminal connected to the first circuit node A. The circuit node B is, in turn, coupled to the fixed voltage reference GND through a third resistive element R3. Again with reference to Figure 2, it can be seen that the electronic circuit 1 also has a second signal circuit portion 3 connected to the power supply line AL in a structurally independent manner of the first power circuit portion 2. Specifically, this second signal circuit portion 3 is coupled to the power supply line AL through at least one controlled switch M1 which may be a P-channel MOS transistor, for example. More specifically, this transistor has first and second terminals respectively connected to the power supply line AL and the signal circuit portion 3, and a control terminal connected to the second circuit node B. The operation of the electronic circuit 1 of this invention will now be described assuming, in particular, an initial state wherein the first Q1 and second Q2 transistors are cut off, and the controlled switch M1 is closed. Under these conditions, the supply voltage Vcc is present on the first power circuit portion 2, whereas on the second signal circuit portion 3 a voltage Vd is present which is close in value to the supply voltage Vcc. As the supply voltage Vcc increases, the voltage across the first resistive element R1 will also increase. Upon the supply voltage Vcc exceeding a given threshold level, the first Q1 and second Q2 transistors change from a cut-off state to a conduction state. In particular, the first transistor Q1 will enable, within the first power circuit portion 2, the protection means arranged to prevent destruction of the electronic circuit 1. The second transistor Q2 will then open the controlled switch M1 to disconnect the second signal circuit portion 3 from the supply voltage Vcc. To summarize, in view of the structural complexity of the signal circuit portion incorporated to a semiconductor electronic circuit being a factor of growing importance, a protection device against overvoltages in the voltage supply as described hereinabove becomes quite convenient to use. It should not be overlooked, moreover, that a semiconductor electronic circuit constructed in accordance with the invention would draw no quiescent additional current, which makes it useful for all those applications requesting quiescent minimal current draw.

Claims: A semiconductor electronic circuit with a protection device against power supply overvoltages, comprising: a power supply line (AL); a reference potential line (GND); a power circuit portion (2) comprising a power supply input and a disabling input; a first transistor (Q1) having a first, a second and a control terminal; a voltage sensor (R1, R2, Z1) having a first and a second sensor terminal and a sensor output (A), said first sensor terminal being connected to said power supply line (AL), said second sensor terminal being connected to said reference potential line (GND) and said sensor output (A) being connected to said control terminal of said first transistor (Q1); wherein said power supply input of said power circuit portion (2) is connected to said power supply line (AL); said disabling input of said power circuit portion (2) is connected to said second terminal of said first transistor (Q1); and said semiconductor electronic circuit comprises a further circuit portion (3) connected to said power supply line (AL) in a structurally independent manner from said power circuit portion (2); characterised in that said further circuit portion (3) is a signal circuit portion; said first terminal of the first transistor (Q1) is connected to said power supply line (AL); a PMOS transistor (M1) is connected between said power supply line (AL) and said signal circuit portion (3); said PMOS transistor (M1) has a control terminal connected to said reference potential line (GND) through a resistive element (R3) and to said power supply line (AL) through a second transistor (Q2); a control terminal of said second transistor (Q2) is connected to said sensor output (A); such that said PMOS transistor (M1) is closed in absence of power supply overvoltage and open in presence of power supply overvoltage. An electronic circuit according to claim 1, characterised in that said first and second transistors (Q1, Q2) are bipolar transistors of the PNP type.

Inventors: BOTTI EDOARDO, MANDRINI TIZIANA, BOTTI, EDOARDO, MANDRINI, TIZIANA
Applicants: ST MICROELECTRONICS SRL, STMICROELECTRONICS S.R.L.
Application year: 1994
Main classification: H02H7
IPC codes: G05F1, H02H3, H02H7, B60R16